Electro-mechanical actuators are used on airborne vehicles and guided projectiles to establish and maintain the positions of position-controlled elements (PCEs), such as fins, flaps and other flight control surfaces. Mechanical power is generated by a motor within an electro-mechanical actuator and coupled to a PCE via a mechanical drive linkage. Control of an actuator is typically managed by a control circuit, or “controller,” which is responsible for accurately positioning the PCE in response to a positioning command. The positioning command may be generated by a navigation system, for example, which is responsible for moving the airborne vehicle or projectile along a desired flight path. In some examples, the positioning command is expressed as an angle, which corresponds to a desired angular position of the PCE.
In a typical arrangement, the controller for an electro-mechanical actuator receives a position command signal as well as a position feedback signal indicating the actual position of the PCE. The position feedback signal may be provided from a Hall-effect sensor within the motor of the electro-mechanical actuator. The controller processes the position command signal and the feedback signal to generate a control signal, which drives the actuator's motor. The controller can thus control the electro-mechanical actuator to establish and maintain the actual position of the PCE at the desired position prescribed by the position command signal.
One general class of controller for electro-mechanical actuators is the proportional-integral-derivative, or “PID,” controller. The PID controller allows a designer to specify parameters of separate proportional, integral, and derivative blocks. Designers can place poles and zeroes in the controller's transfer function to compensate for dynamics of the motor and the electro-mechanical actuator, for establishing stability and desired response characteristics. The use of PID controllers in connection with motors is discussed, for example, by R. Krishnan in “Electric Motor Drives Modeling, Analysis, and Control,” Prentice Hall, N.J., 2001.
Other classes of controllers for electro-mechanical actuators include optimal and adaptive control schemes. Optimal controllers show an advantage over PID controllers where the design goal is to provide an optimized control effort within an assumed range of parameter variations. Adaptive controllers, such as gain-scheduled controllers, can vary their parameters to adapt to changes in their operating environments.